This invention relates to a display device for electronic apparatus, and in particular a display device for electronic apparatus, such as an electronic timepiece, including an electronic device required to be maintained always in an operative state.
With the recent advancements of electronic techniques a variety of mechanically driven devices are gradually being replaced by electronically driven ones. Of instruments incorporated in an automobile, for example, a timepiece is being replaced by an electronic one having a light emitting display unit. The use of such an electronic device increases the dissipation power of an automobile battery and, because of a limited capacity of the automobile battery, electronic devices incorporated into the automobile are designed to make the dissipation power as little as possible. Since the electronic timepiece must be maintained always in an operative state, it is necessary to sufficiently lower the dissipation power of the electronic timepiece. Such an electronic time-piece has a light emitting display device adopted to provide a visual time indication in a digital fashion. The light emitting display device is so constructed to display time indication only when a time display is required. For example, when the automobile is stopped or parked, only a display information generating circuit such as a time information generating circuit of the electronic timepiece is operated and a supply of electric power to the display device is interrupted. In the conventional electronic timepiece, however, a power supply to the display device is effected by disconnecting the automobile battery, and a digit drive signal from a driver in a display information generating circuit of the electronic timepiece continues to be supplied to an amplifier circuit which is constructed of emitter grounded transistors and connected to a display unit in the display device. For this reason, a leakage current continues to flow through the base-emitter paths of the transistors in the amplifier circuit. In consequence, the electronic timepiece connected to the automobile battery dissipates a leakage current and an electric current through the time information generating circuit which needs to be maintained always in an operative state. This causes the automobile battery to overcharge.